An integrated circuit (IC) package assembly may include one or more dies coupled with a package substrate by interconnect structures. An underfill material may be deposited between one or more of the dies and the package substrate. The underfill provides stability and mechanical strength to the package by reducing a Coefficient of Thermal Expansion (CTE) mismatch between the die(s) and the package substrate and interconnects, and by providing structural support to the package.
Emerging underfill materials may include filler particles that are configured to further mitigate the effects of the CTE mismatch. However, the filler particles may settle away from a surface of the dies during flow and/or curing of the underfill material resulting in a non-uniform distribution of the filler particles between the dies and the package substrate. For example, the filler particles may settle away from bond Cu pads formed on the die such that the effects of CTE mismatch are not mitigated in these regions.
As a result, such filler settling may result in reliability failure associated with CTE mismatch such as, for example, delamination around the interconnect structures, which may further result in the formation of a crack in the underfill material. The crack may extend to the IC of the dies, which may lead to failure of the IC package. As the bump pitch scaling goes down, the risk of UF/Cu bump delamination and UF cracking caused by the filler settling increases.